Site News  |   Monitor Keywords  |   Monitor Archive  |   Organizer  |   Account Info  |

Device for improving the charging or discharging process of a battery

Device for improving the charging or discharging process of a battery description/claims

The present invention relates to a device to improve the charging or discharging process of a battery, to increase the usable capacity and the usable lifetime (number of cycles) of a battery.

Using balancing for charging/discharging batteries is known from prior art.

U.S. Pat. No. 6,114,835 for example discloses a balancing circuit that incorporates a voltage threshold which determines when to initiate a charge balance mode in order to equalize the level of charge in at least two cells of a multi-cell battery pack. Thereby balancing is initiated when the voltage level of a first cell reaches a first threshold voltage and balancing is stopped, when reaching a second threshold voltage. Balancing is used during charging a battery to balance the charge between cells. This can be done using passive balance circuits or active balance circuits. Normally the balancing method/balancing procedure is started at the end of charging, when one or more of the cells reach prematurely the end of charge voltage or during charging, when one cell voltage reaches a predefined fixed threshold. Then the balance circuit will equalize the charge of this cell compared to at least one of the other cells.

It is a drawback of this device that balancing is only applied between two specific thresholds and that it is only applicable for charging a battery. Furthermore the equalization takes a long time since the threshold is fixed at a certain value.

Patent application US2005/0140335 discloses a terminal voltage equalization circuit to equalize the terminal voltage of a series of connected battery strings. This patent application states that the charging current of the higher charge cells is reduced and the lower charged cells are equalized, making it therefore clear, that they use their concept during charge only. It is a further drawback that balancing is used on certain time intervals only.

According to prior art there are several methods and devices known to determine the state of health or the age of a battery. The internal battery resistance for example is a very good indicator for the state of health (or age) of the battery. Common methods for the internal resistance measurement are either the AC Impedance measurement, where a medium to high frequency signal is used to measure the impedance or the DC Resistance measurement, where with an additional circuit a DC current is used to measure the voltage drop and calculate the DC resistance. The latter is used off-line, meaning, that when the battery is not used, the cell is discharged with a constant current and the voltage drop is measured. To get an accurate reading the discharge current has to be in the order of half or full nominal battery current. This is not an energy problem as the pulses are quite short, but the measurement current has to be switched on (needs large semiconductor switch).

An object of the present invention is to provide a device for monitoring a battery comprising two or more cells in series and to keep the charge imbalance between the cells within a narrow band using a balanced scheme that does not have the disadvantages of prior art as already mentioned.

It is another object of the invention to provide a method and a device that is able to reach a full charge of a battery in a shorter time than methods and device of prior art.

According to invention there is provided a device for balancing a plurality of at least two batteries or cells of a multicell battery comprising a multicell battery and a battery management system with a balancing circuit. The device is characterized in that all individual battery cells are connected to a battery monitoring system, wherein the monitoring system measures every single cell voltage as well as the battery temperature and the current. The said battery monitoring system is able to discern a charge imbalance between the cells of a multicell battery (e.g. discern the lowest cell voltage or when the voltage of one or several cells is below the average voltage of all or when one or more cells are outside a statistical tolerance band given by the standard deviation) and to discern a number of cells having a voltage higher than a determined maximum allowable voltage, which will be balanced until the charge imbalance decreases to an acceptable amount. The battery management system is active during charging and discharging of said multicell battery, wherein the thresholds vary with the state of the battery. These measurement values are used for various calculations described below.

The balancing method is applicable on the directly measured cell voltages as well as on the corrected cell voltages according to the method. The advantage of using the corrected voltages is that these voltages are equivalent to the charge of the specific cell whereas the uncorrected values are influenced by the current and the temperature and the age of the battery, which may lead to unintentional balancing of certain cells with an internal resistance that differs from the average internal resistance inside the battery pack. This leads to a more efficient balancing, especially for batteries with a higher number of cells in series.

The battery monitoring system of the device effectively monitors all individual cells continuously or intermittently. If inconspicuous cells are checked, the battery monitoring system can store a value stating that the voltage of a given cell is far away from, i.e. lower than, the upper threshold and is also in its voltage quite higher than the lowest voltage in question. Such cells can then be omitted in a continuously running check and can be checked intermittently with a lower frequency. Such cells will then be reallocated to the usual check frequency, if their values approach the given limits.

The drawings will be explained in greater detail by means of a description of an exemplary embodiment, with reference to the following figures:

FIG. 1 shows a flowchart for a balancing method according to the present invention;

FIG. 2 shows an arrangement of an online internal resistance measurement according to the present invention; and

FIG. 3 shows an arrangement of a device for cell voltage correaction according to the present invention.

• Provisional Patent
• Utility Patent

• What Is a Patent?
• What Is a Trademark or Servicemark?
• What Is a Copyright?
• Patent Laws